Secondary AC Resistance to Ground Measurements
Subject: Secondary AC Resistance to Ground Measurements
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Sat, 24 Jul 1999 22:21:12 -0600
I have been using my new HP34401A multimeter to measure the resistance of
my secondary system.
I have found some fascinating things!!
Using a very high Q ATC 40.8pF cap in series with my secondary, I have
found that the AC resistance of only the secondary coil is 391 ohms (the DC
resistance is 70 ohms of that).
When I run the secondary without any top terminal, the measurements show
that the Cself resistance has 661 additional ohms to ground. In other
words, Cself is in series with 661 ohms to ground for a total of 1052 ohms!!
When I add my small torroid and subtract out the parallel Cself resistance,
I find that my small torroid has 594 ohms to ground. Adding this parallel
resistance to the Cself resistance gives a total resistance to ground of
312 ohms plus the 391 ohms of coil AC resistance.
When I add my large torroid and subtract the parallel Cself resistance, I
find that my large torroid has 136 ohms to ground! for a Total of 112 ohms
plus the 391 ohms of coil AC resistance.
This may be really significant! The large torroid apparently is so large
that it couples to the surroundings with a fairly low resistance. The
lower resistance lowers the losses in the secondary system dramatically!
This could easily explain why large torroids give so much better arc
performance. This also suggests that the AC resistance of the secondary is
not a big deal with small torroids but could be very significant with large
torroids. I think this will all match the observations. A large torroid
gives better arcs do to lower losses through better coupling to ground.
The secondary coil resistance is significant with large torroids but less
so with small torroids. A large torroid with thick low loss secondary coil
windings should have the lowest loss and give the best arcs...
I have updated my LTR MicroSim Models to reflect these new things:
A new total system schematic for my coil is also at:
This is all really new (like an hour old) but I think I am on the right
Much to ponder here...